Method of making high silica glass



Patented Aug. 15, 1944 UNI-TED sTA E s PATENT OFFICE METHOD OF MAKING HIGH SILICA GLASS Martin Emery Nordberg, Corning, N. Y., and

Harold Edward Rumcnapp, West Los Angeles, C'alif., assignors to Corning Glass Works, New York, N. Y., a corporation of New York No Drawing. Original application July 20, 1940, Serial'No. 346,654; Divided and this application May 29, 1943, SerialNo. 489,064 7 3 Claims. (Cl. 49-79) "berg, there is disclosed ,a method of making a highly siliceous glass which comprises melting a glass, fabricating'the same into a fixed shape, heat treating the shaped article to cause throughout its mass a molecular rearrangement resulting in'the formation, ofv two interdispersed term, are hereinafter referred to as phases. One phase is highly siliceous and substantially insoluble. The other is soluble in acids and is thereafter leached out leaving a'highly siliceous, rigid,

porous structure having the same shape as the initial article. The resultant article is thereafter fired to close the pores and form a vitreous transparent glass. Such glass'has a silica content of over 93% and a thermal expansion coefficient from about 7 X 10* to about 14x 10 or slightly above 'that of, pure vitreous silica. As shown in the patent, any coloring oxides or agents present in the initial'glass are substantially removed during the process and the final glass is practically colorless.

The primary object of this invention is subsequently to alter the physical characteristics of such finished glass.

Another object is to alter the spectral characteristics of the glass without substantial change in heat resistance, thermal expansion coefficient and other properties thereof.

The above and other objects may be accomplished by practicing our invention which embodies among its features impregnating the porous article, after extraction 'of soluble constituents, with a metallic compound which is decomposable by heat, and thereafter firing it.

Another feature comprises treating the porous article with a solution containing a salt of 9. metal which will color glass or fluoresce therein and firing the article. a

glass as by printing or stamping a solution of the salt on the porous glass in the desired design.

In practicing our invention the article is fabricated in the usual manner from a glass containing 60% to 82% SiOz, to 35% B203, and 5% to 10% alkali oxide, the composition being governed by considerations set forth in the above compositions which, for lack of a more accurate mentioned patent. In these glasses. alumina may be present in small amounts and its presence in amounts up to 4% in glasses of lowsilica content located near the center of the defined field is advantageous in facilitating the subsequent leaching of the glass.

The article is subjected to a heat treatment which comprises heating the glass at a temperature between about 525 and 600. C. for: a'time necessary to cause the required change in structure. Asa result oftheheat treatment the glass will become more or less completelyseparated or formed into two phases, one of which is very rich in boric oxide and alkali and is soluble in acids and the other of which is very richin silica and is substantially insoluble in acids. In other words, a change has taken place in the structure of the glass so that the constituents other than silica are for the most part soluble in acids and may be extracted thereby.

The previous thermalhistory of a glass has a bearing upon the heat treatment which may be required for best results. Articles which are relatively thick receive some heat treatment in nor- -mal working and cooling and the additional heat treatment required may be different from that required by a thinner article which was cooled more quickly during manufacture. Hence the term fheat treatment as used herein includes heat treatment during fabrication as well as any additional heat treatment following fabrication.

In order that the leaching step may be carried out with better facility it is desirable, particularly in the case of pressed ware, to etch off the surface of the glass by immersing it for a few minutes in a dilute solution ofhydrofiuoric acid or in a hot 5% sodium hydroxide solution.

The article is then rinsed and immersed in dilute hydrochloric, nitric, or sulfuric acid, thetemperature of the bath being held preferably at or near its boiling point to obtain maximum speed of extraction. The progress of the extraction may be observed because the interface between the extracted and unextracted portions of the, glass is visible, Instead of carrying the extraction to completion, it may be stopped when any desirable depthhas been reached by removing the article from the acid bath.

After theacid treatment the glass is washed to remove all traces of the soluble constituents which have been acted on by the acid. This is best accomplished by immersing the glass for several hours in pure running water so as to ex-' pose all sides of the article to the washing action. The removal of the soluble phase leaves the silica shape. of the article, but submicroscopically porous, thepores being filled. with water.

We have discovered that metal. salts .orcom pounds can-be introduced ina uniform-distributionthroughout the pores or confined-tea limited portion. thereof'after which the article can be dried and fired. to close the pores and produce a non-porous, vitreous glass article having. the shape-of the initial glass article. though somewhat'smaller in size and. having, ln-thosdpor tions containingv the. metal, a selective spectral. transmission or color. If thewholefarticle isto be colored, this is best accomplished byimmers:

ing the washed-porous article in. a solution of, the desired .metal 1 salt. for. a, time -sufiicient to. permit the .saltsolution to. difiuseinto the pores... An. immersion. for .two. hours. was suflicient 1 for' complete diffusion into-a. slab of the porousmaterial one-eighth inch in thickness. This .diiifusionwas about, ten times .as rapid when a pre+ viously dried porous sample wasused; If -it is desired, .to restrict the. area, of, the glassto be colcred as for the purpose. of forming a design the article is-first .dried. and themetal salt solution. isthen appliedinthe .desired. design: by 'means of; a brush. or a stamp-or. a silkscreen- .or. the like..

' For this purpose the viscosity of the-solutionmay .beincreased by the addition thereto or .a .viscous liquid such as glycerine. 7

, Afterthe porous glass has beenimprgnated with the metal salt, it is dried by evaporating-- from the poresthe solvent in--.which-the metal I salt. was dissolvedthe temperature is increased to 900 -1150 C.

f where it is held for ashort time after which the article may be cooled asrapidlyas desired,

Our researches show that practically any colored cation canthus be introduced into the (pores and thearticlethereafiter.fired to a non-porous colored glass. It has further been found that for agiven-firing temperature, if. an excessive amount ofqthemetal salt is used, the resultingcolored glass will not be transparent but will be acolored opal glass, that is, will havelight diffusing characteristics. The higher themaximum tempera ture at which-the article is fired, the greater the 7 amount of metal salt that must beintroduced to cause .opalescence. Articles having a shape which permits their being supported against warping or deforming may be' fired. at temperatures as high above 1500 C. The amount of the salt which is absorbed is easily controlledby varying the concentration of the salt in the-solution into which the-porous glass is immersed; The maximumconcentration which will produce a transparent colored glass, will not only depend uponthetem- V perature of firing'but' willvarywith': salts of. different metals and will vary also with differentsalts of the same metal.

For example, when small plates of a porous glass, prepared. by. the

above describedmethod from a glass of the initial In doing this. a..moderate I heat may be employed, but care shouldbe exer-.. cised against expelling the solventtoorapidly because an explosive evolution of thevapor may .cause the article to spall or crack; After drying,.

pha'seas a rigid. structurepossessing the ori in l;

trations intermsofthe oxides of the respective metals and. the, color of the resulting. glass.

dov the concentrationsof. the solutionsin terms of-v oxide" vary with; respect toqthe metal ernployed but, also, as is shownin thecases of .co-

bait. and chromium,.the oxide concentrations vary with; respectstov theparticular salt ofthe metal. This.phenomenonisnot understood, but is believed to be. caused byra selective absorptiveeffect of? the anion..of therespective salts. The above recited. maximum: concentrations for producing-transparent glasses at a firing tempera- .tureof 1150 C. are.i-ncreased somewhat when a firing; temperature. of 1300 C. is employed. For example, the maximum.- concentration of nickel nitrate fora firing: temperature. of l300 C. is aboutz10% by weight, for copper nitrate a little over 13%, for cobalt nitrate over 12%, for cobalt chloride 13%.forferricnitrateover 15%, etc. The color or hue which is produced. by a given metal in the finished product is substantially the samewhether the nitrate, chloride, or sulphate is used. The color saturation or density varies directly with the concentration ion.

ofthe coloring In other words, various salts of the same metal; will producesubstantially :the same hue .55. C., while articles which are subsequent.-

ly worked ina fiame may attain temperatures but the saturation or density of the color will de-' crease, as the solutions are made more. dilute. The chromium compounds,.CrO3, NHrCr SOr)z, CI2(SO4)3, NH4C1O4, and .ClCla in Water solutionscontaining each an amount of the respective saltxequivalent to, 1% by weight of CrzOs, produced .each. substantiallyv the same hue in porous glass plates treated therewith. and fired.

The porous glass may also be treated in a solution-containinga combination of two or more metal salts and thereafter dried and fired to pro- 'duce a glass colored by the combination of metals. For example, pieces of porous glass were treated with solutions containing both copper nitrate and cobalt nitrate. The resulting colors were different from those produced by either copper alone or. cobalt alone. The ratio of copper to cobalt determines the particular hue which is obtained.

The glasses resulting lfrom treatments with the solutions shown inthe above table are all transparent but with solutions of these salts in con-.

centrations greater than aboveset forthv the resulting glasses will be opal and will have light difiusing characteristics. For some purposes light diffusing characteristics are desirable, but if it is desired to obtain a-grea ter saturation or density of color than can be obtained with the above recited maximum concentrations, we have found that this can be. accomplished ,by introducing into the glass-along-.with the metal salt: solution asolution of another saltor compound, hereinafter called clearing agent; which has the effect of increasingthe amount of. metal salt that can be introduced without causing opalescence. The

number-of compounds which have a clearing eifect is'very limited and we have found that From'the above it will be notedthat not only.

assume aluminum nitrate, phosphoric acid, and alkali salts possess this property in substantial degree. Presumably other salts of aluminum will also be effective and we have iound that alkali phosphatcs, such as sodium dihydrogen phosphate. are very efficient. The presence of no in the glass may also have an effect on the ultimate color. It tends to bleach the color oi iron and it causes a change in hue oi the colors produced by nickel and cobalt. Alkali salts in general tend to cause devitrification and spelling of the glass on firing due to the tendency of such salts, when too concentrated, to creep or come to the surface on drying. illustrates the effect of aluminum nitrate and phosphoric acid as clearing agents.

Three plates of the above described porous glass were treated as follows:

One was immersed for 24 hours in a water solution containing 10% by weight of and was thereafter dried and fired at 1150 C. After firing, this sample was a dense opal.

The second sample was immersed for the same length of time in a water solution containing the same percentage of nickel nitrate and containing alsoan amount of A1(NO3) 3-91-3120, equivalent to 5% by weight of A1203, and was thereafter fired at 1150 C. After firing, this sample was transparent and the color density was considerably greater than that produced by the maximum concentration recited in the above table.

The third sample was immersed for the same length of time in a water solution containing the same percentage of nickel nitrate and containing also an amount of HsPO4, equivalent to 5% by weight of P295, and was thereafter fired at 1150" C. After firing, this sample was transparent and although the color saturation was greater than that of the maximum concentration of the above table .the hue was different, being in this instance a bright amber yellow.

Subsequent analysis of the samples showed;

M0, the second contained 56% NiO, and the third contained that the first contained .42%

.4l% NiO, thus demonstrating that the effect of the aluminum salt or the phosphoric acid was not to reduce the amount of nickel ion adsorbed by the, porous glass but to exert some specific clearing action.

If porous glass articles after treatment with a. metal salt solution are fired in a reducing at-. mosphere, unusual color effects can in some cases be obtained. Under strong reduction most metal salts in such glasses are reduced to metal and give the glass a smoky black appearance. Some metals, however, produce a useful and unique coloration. For example, a glass that has been treated with a solution of a molybdenum salt, when fired in an atmosphere of hydrogen, becomes a lustrous, glossy, opaque black throughout its mass. A glass treated with a vanadium salt and fired in hydrogen takes on a beautiful sky blue hue.

If desired, the absorption or introduction of The following experiment the metallic salt solution into the porous glass can be confined to any particular area oi the article to produce therein any desired design.

This is accomplished by increasing the viscosity 0! the solution by the addition oi a viscous liquid such as glycerine and applying the viscous solution to the selected areas or a stamp. The well known silk screen process may also be employed for this purpose. Best results are obtained by first drying the porous glass before the application of the solution. In this manner various intricate designs and deccorations may be formed within the surface of the article in which several colors may appear due to the successive application of different metal salts. An article may thus be produced which is of one color on one face and a different color on its other face.

Glasses which have been prepared in accordance with the above described method show the characteristic fluorescence of the metal which was introduced when such glasses are irradiated with ultraviolet light and other exciting radiations. It will thus be seen that fluorescent screens can be prepared in which intricate multicolored designs can be caused to change intermittently incolor and appearance by alternately transmitting visible and ultraviolet light therethrough.

We claim:

1. The method of making a glass article, which comprises melting a, glass, fabricating the same into a fixed shape, heat treating the article to render constituents other than silica soluble; dissolving out major quantities of the said other constituents to leave a highly siliceous, substantially transparent, porous article, impregnating at least a portion of the porous article with a solution containing a salt of a metal which will color glass and a compound of phosphorous and drying and firing the "article to close the pores and. incorporate the metal into the glass.

2. The method of making a glass article, which comprises melting a glass, fabricating the same into a fixed shape, heat treating the article to render constituents other than silica soluble, dissolving out major quantities of the said other com stituents to leave a highly siliceous, substantially transparent, porous article, impregnating at least a portion of the porous article with a. solution containing a salt of a metal which will color glass and phosphoric acid, and drying and firing the article to close the pores and incorporate the metal into the glass.

3. The method of making a glass article, which comprises melting a. glass, fabricating the same into a fixed shape, heat treating the article to render constituents other than silica soluble, dissolving out major quantities of the said other constituents to leave a highly siliceous, substantially transparent, porous article, impregnating at least a portion of the porous article with a solution containing a salt of a metal which will color glass and sodium dihydrogen phosphate, and drying and firing the article to close the pores and incorporate the metal into the glass.

MARTIN EMERY NORDBERG. HAROLD EDWARD RUMENAPP.

by means or a brush 

